1. Field of the Invention
The present invention relates to an image processing apparatus and, more specifically, to an image processing apparatus to be incorporated into a machine tool, such as a punching machine, for detecting and determining machining points by image processing, incorporating improvements in the image forming accuracy of a camera unit for taking detection marks indicating machining points and the like.
2. Description of the Prior Art
A conventional image processing apparatus has a camera unit comprising a lens system including a filter through which incident light, namely, light reflected by or transmitted through a detection mark (reference mark), is received, lenses and a diaphragm, and a photodetecting device, such as a CCD, disposed behind the lens system so that the incident light is focused thereon. The image processing apparatus is set with its optical axis inclined at a predetermined angle to a perpendicular line to a plane including a detection mark.
This image processing apparatus is set with its optical axis inclined at a predetermined angle to a perpendicular line to a plane including a detection mark, such as a circle or a cross, formed on a flat work, such as a plate, when the punch of a machine tool, such as a punching machine, is disposed on the perpendicular line to the plane including the detection mark and it is impossible to set the camera unit on the perpendicular line. The image of the detection mark received through and focused on the photodetecting device by the lens system is analyzed by a controller connected to the photodetecting device to calculate data for operating the machine tool and to control the operation of the machine tool.
Since the camera unit of this conventional image processing apparatus is set with its optical axis inclined to the detection mark formed on a plane, a light path between the camera unit and a portion of the detection mark nearer to the camera unit and a light path between the camera unit and a portion of the detection mark farther from the camera unit are different from each other in length. Therefore, portions of the image of the detection mark focused on the photodetecting device farther from the center of the detection mark are inferior in sharpness to portions of the same nearer to the center of the detection mark, and such portions having inferior sharpness makes the subsequent image analysis and calculation inaccurate.